The present invention relates to a new and improved construction of a centrifugal separator, and, more particularly, to an improved design of pusher centrifuge.
Generally speaking, the pusher centrifuge of the present development is of the type comprising at least one sieve or filter drum rotatably mounted within a housing. Further, there is provided a substantially disk-shaped pusher or thrust member, typically in the form of a pusher or thrust floor member, which is arranged within the sieve or filter drum and essentially coaxially with respect thereto. This pusher floor member is rotatable and may be advantageously constructed to be displaceable to-and-fro between deflection or turning points relative to the sieve or filter drum in the lengthwise direction thereof. This pusher floor member wipingly moves along a longitudinal section of a sieve or filter surface of the sieve or filter drum and displaces a filter cake, i.e. the solid materials of the treated product along the sieve drum in the direction of outlet or discharge openings provided for the filter cakes.
Typical examples of centrifugal machines or separators have been disclosed, by way of illustration, in U.S. Pat. No. 1,928,341, granted Sep. 26, 1933, U.S. Pat. No. 1,944,391, granted Jan. 23, 1934, and U.S. Pat. No. 2,232,769, granted Feb. 25, 1941.
The generally known advantages of pusher centrifuges, such as higher product throughput and small residual moisture content, are counterbalanced by the drawback that the centrifuge only can be supplied with relatively high solid concentrations. If the infeed or input concentration of the product which is to be treated decreases, then there is present the danger of so-to-speak "flooding" the centrifuge. Under the expression "flooding", as used herein, there is intended to describe the operating condition where the dewatering or dehydration time between two strokes of the pusher floor member is insufficient to dewater the sump forwardly of the pusher floor member to such an extent that the filter cakes, i.e. the solid materials of the treated product can be transported. In the context of this disclosure the term "sump" is intended to designate the longitudinal section or portion of the sieve or filter drum which is wipingly contacted by the pusher floor member. In the event the dewatering or dehydration of the processed product is not sufficient, then there is still located within the sump, during the return movement of the pusher floor member, a suspension which can not be displaced in the form of a filter cake, so that there arises the aforementioned flooding.
In order to solve this problem, i.e. to obtain a sufficient dewatering action in the sump, various attempts have been made to incorporate additional sieve or filter surfaces in the centrifuge along the path of the suspension which is to be separated towards the sump. However, it was not heretofore possible with these facilities or measures to enlarge the field of application of the pusher centrifuge in terms of handling thinner suspensions.
When processing suspensions which tend to sedimentate relatively well such thin suspensions are initially concentrated by statically sedimentating the same and only thereafter are they inputted to the pusher centrifuge. In the case of suspensions which tend to sedimentate rather poorly there are used for the pre-concentrating operation possibly other machines, such as for instance centrifugal decanters, by means of which it is possible to also process thin suspensions. Yet, these systems are quite complicated in construction, and accordingly, rather expensive, frequently also tending to be problematic as far as the servicing and maintenance thereof is concerned.